Method for manufacturing unitary stem and plug-in bases for electron tubes and the like



Nav. 23, 1943. Q [LLER 2,334,784

METHOD FOR MANUFACTURING UN RY STEM AND PLUG-IN BASES FOR ELECTRON TUBES AND THE LIKE Original Filed Nov. 20, 1957 \(EXPAN LE 7 CHI/C co/VMAcT/BLE AND /4 :1. EXPA/Vs/aLE CHUCK MOLD) m vE/vTaK Patented Nov. 23, 1943 METHOD FOR MANUFACTURING UNITARY STEM AND PLUG-IN BASES FOR. ELECTRON TUBES AND THE Carl F. Miller, Corning, N. Y., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Original application November 20, 1937, Serial No. 175,619, now Patent No. 2,250,183, dated July 22, 1941. Divided and this application March 22, 1941, Serial No. 384,660

Claims.

can be sealed through the stem-base with a minimum of shrinkage.

A feature relates to the method of sealing a plurality of rigid metal contact prongs directly into a composite stem-base, and without employil'lg any special grading glasses or beads between the prongs and the body of the stem-base...

Another feature relates to an improved method for directly sealing a plurality of rigid metal contact prongs into a composite stem-base of a radio tube, whereby low density areas of glass around the prongs are avoided.

Another feature relates to an improved method of forming a composite stem-base for a radio tube with the rigid metal contact prongs sealed therein in a vacuum-tight manner and disposed around a common center.

Other features and advantages not specifically enumerated will be apparent after a consideration ofthe following detailed descriptions and the appended claims.

In the drawing, which represents typical embodiments of the invention,

Fig. 1 is a view partly in section of the lower, portion of a radio tube embodying features of the invention.

Fig. 2 is a bottom plan view of Fig. 1.

Fig. 3 is a diagrammatic view of apparatus that may be used to form the composite stem-base of Fig. 2.

Fig. 4 is a sectional view of Fig. 5 taken along the line 4-4.

Fig-5 is a modification of the stem-base of Fig. 1.

Fig. 6 shows a modified apparatus for forming the composite stem-bases. 4 It has been the usual practice in radio receiving tubes of the glass bulb type, to employ a separate pronged member which is fastened to'the bulb, usually by a special basing cement. In other'words, the evacuated or gas-filled glass bulb is usually provided with a reentrant stem terminating in a substantially flat press wherein the relatively thin and soft lead-in wires are sealed. This construction ,has a number of drawbacks which increase very materially the cost of manufacture. One of these drawbacks is that because of the flat nature of the press it is' possible to z .vided with a skirt or rim 5.

seal the lead-in wires therein in substantially only a straight line. Consequently in order to make a radio tube of relatively small dimensions, it is necessary to have a relatively small press, and therefore the lead-in wires must be of correspondingly small diameter. Inasmuch as practically all radio receivers are equipped with tube sockets of a standard type, that is with the contacts arranged around a common center, it becomes necessary to attach to the tube per se, the separate pronged base mentioned above. the separate base is usually of Bakelite or similar material it is not feasible to exhaust and seal the tube under the ordinary exhaust schedules, with the base attached thereto, because the temperature of the exhaust schedule would ruin the material of the base. For these and other reasons, it is necessary after exhaustion and sealing of the tube, to subject it to an entirely separate basing operation. Apart from the increased cost of the base itself, is the cost of the basing operation which requires that the bulb be axially aligned with the base, and then the relatively thin lead-in wires must be threaded into the contact prongs carried by the base and then soldered thereto.

There is disclosed in U. S. Patent No. 2,238,025 a tube structure in connection with which the present invention is applicable wherein the con tact prongs are directly sealed through the glass base or bottom of the bulb.

I have found that in order to produce the most effective vacuum-tight seal between the contact prongs and the glass base, it is important to avoid any areas of glass of low or non-uniform density in the regions where the prongs are sealed. For this purpose there is shown in Fig. 3 the preferred manner of effecting the seal-in. A previously prepared glass blank I of the shape shown in Fig. 3 is provided with'a central opening 2 to receive the exhaust tubulation. and a series of smaller openings 3 to receive the rigid contact prongs 4. Preferably the blank is pro- The prongs 4 are placed in the corresponding openings in the lower chuck member 6 which may be carried by a ro-.

Since around the blank or the glass may be heated by electrical means.

I have found that in order to attain the required uniformity of glass density around each prong, it is necessary that the glass be heated uniformly, as for example by burners B, where it is to contact with the prong during the sealing operation. For this purpose, it is preferable to make the openings 3 in the glass blank of tagradient is attained in the area of the glass adjacent each prong.

.When the glass becomes plastic, the expansible chuck member I of any well-known construction as described for example in Hawkins Mechanical Dictionary, published by Theodore Audel 8: Company, page 221, and the shaping member 8 are lowered, whereupon the chuck I is expanded radially in any well-known manner thus forcing the molten glass radially outward and compressing it against the contact prongs which are wetted' thereby. If desired, the chuck members 6, I and 8 may be heated to prevent strains being formed in the glass when these parts contact therewith as above described. The chucks are then separated and upon cooling and annealing in any ,wellknown manner the formed base is removed, with the prongs effectively sealed therein in a vacuumtight manner. The glass blank is thus provided with an annular shoulder 9 into and through which the contact prongs 4 are directly sealed. Because of the radial pressure exerted on the molten glass by the expansible chuck I, the glass is distributed around each prong with substantially uniform thickness and uniform density. It will be understood of course that the prongs may beoxidized prior to their insertion into the chuck 6, to facilitate sealing as described in U. S.

Patent No. 2,219,574.

A short length of exhaust tubing l0 '(Fig. 1) may then be sealed to the portion H of the base, in alignment with opening 2 and tipped-off in any well-known manner after the bulb has been evacuated. Any well-known type of radio tube mount or electrode assembly may be connected to the upper ends of prongs 4 whereupon the glass bulb or envelope I2 is assembled over the mount and sealed to the skirt 5, as partially shown in Fig. 1.

It will be noted that after the exhaust tubulation I0 is tipped-oil, it is protected throughout the greater part of its length by the annular rim 9, and if desired the tubulation may be tipped-off so that it does not extend downwardly beyond the said rim.

Instead of forming the rim 9 with an annular wall of uniform thickness, as shown in Figs. 4 and 5 this rim may be formed with increased thickness at the regions where the prongs are sealed therethrough, as indicated by the numeral I 3.- It will be understood of course that the outer face of the expanding chuck I and the inner face of member 8 will be shaped to produce the shape of the rim 9 as shown in Figs. 4 and 5.

Instead of employing an inner expansible chuck such as chuck I, and an outer shaping member 8, thus forcing the molten glass radially outward, the glass may be forced radially inward. Such an arrangement of apparatus is diagrammatically shown in Fig. 6. In this embodiment the member I4 may be a simple plunger. The outer annular shaped member I5 is made up of a plurality. of chuck jaws which are capable of being forced inwardly in the direction of the arrows to compress the molten glass radially inwards against the contactprongs. In the event that both inward and outward radial pressures are desired, then both the member I4 and the member l5 may be expansible, so that as the member I4 is expanding radially outward, the member I5 is being contracted radially inward. Thus member 14 may be a radially expansible member similar to the member I (Fig. 3). In either of the embodiments of Figs. 3 or 6 the members 1, 8 and the members l4, l5, may be rotated during the expanding operations, if desired.

The composite stem-base formed as above described may be incorporated in any well-known type of radio tube, for example of thetype disclosed in U. S. Patent No. 2,250,184.

While certain specific embodiments of the inventive method have been disclosed, it will be understood that various changes and modifications may be made therein. The term wetting temperature as employed herein is used in its meaning as well understood in the glass-to-metalseal art, and means that the glass is'raised to a sufficient temperature so that the metal surface intermingles with the glass in the intimate manner required for producing a satisfactory vacuumtight seal.

This application is a division of application Serial No. 175,619, filed November 20, 1937, issued as U. S. Patent No. 2,250,183.

What I claim is:

1. The method of forming a composite unitary stem and plug-in base which comprises forming a glass blank with an integral annular shoulder having a plurality of discrete preformed perforations spaced around the margin of the shoulder, inserting rigid metal rods in corresponding perforations with the rods extending outwardly on opposite sides of the blank, heating the shoulder in the regions where the rods pass therethrough to render it plastic, and pressing the plastic glass into sealing engagement with said rods by a force acting substantially entirely perpendicularly to the rods.

2. The method of forming a composite unitary stem and plug-in base of the type having an annular shoulder which comprises inserting a plurality of rigid metal rods through individual preformed perforations and arranged around the margin of a glass blank passing through said shoulder, uniformly heating the glass of the blank preforming said shoulder with a series of discrete circumferentially spaced perforations, assembling a rigid metal rod in each of said perforations, heating the shoulder adjacent the rods to the wetting" temperature, locating said shoulder between inner and outer shaping members, and

moving one of said members radially against the shoulder to compress the glass of the shoulder around said rods.

4. The method of forming a composite stembase for an electron discharge tube which comprises forming a glass blank with a circular skirt and an integral annular shoulder, inserting a plurality of rigid metal rods through preformed discrete perforations in said shoulder, heating said shoulder adjacent the rods and compressing it prongs being arranged in a closed path around the center of the blank, and melting the region of the blank around each prong to force it into sealsubstantially entirely in a radial direction into 10 1118' e flfl t the ewithsealing engagement with said rods. I 

